The present invention relates to an offset printing press.
Presses of this kind are already known which essentially consist of an engraved cylinder tangential to a blanket cylinder or transfer cylinder of flexible material and a cylinder known as the counterpart, in contact with the blanket cylinder, the sheet of paper to be printed moving past between the blanket cylinder and the counterpart cylinder.
In a known machine of this type the blanket cylinder and the counterpart cylinder are supported by two vertical side plates mounted on the frame of the machine in such a way that they can slide longitudinally and horizontally, so as to place the blanket cylinder in contact with the engraved cylinder, causing the two side plates to slide horizontally, a device being provided for converting the horizontal sliding movement of the two side plates into a vertical movement of the counterpart cylinder positioned underneath the blanket cylinder, in such a manner that the counterpart cylinder is always placed in contact with the lower part of the blanket cylinder when this latter itself has been placed in contact with the engraved cylinder. The operation of changing the size can thus be carried out very rapidly, as the operation of placing the blanket cylinder in contact with the engraved cylinder, borne by the frame, automatically fixes the counterpart cylinder in position against the blanket cylinder, whatever the size concerned. A machine of this known kind, however, suffers from the drawback of comprising two distinct mechanisms, one for the change of size and one for the operation of fixing the cylinders against and detaching them from each other.